The present invention relates, in a general fashion, to couplings, in particular for loading arms.
As is already known, a coupling is a mechanical assembly comprising clamping modules, intended in particular to apply a clamping preforce so as to ensure the mechanical linkage and tightness between an articulated arm for loading and unloading products, in particular fluid products, such as for example petroleum products (liquefied natural gas etc.), and a complimentary means installed on a vessel.
The present invention is more particularly aimed at the case where the coupling is a hydraulic coupling with several clamping modules, in practice three or more, capable of conveying liquid products, in particular at very low temperatures (up to −196° C.).
According to an arrangement which is already known, each clamping module comprises a clamping jaw for clamping which is designed to couple the arm to a complimentary means, such as a manifold, and, for this clamping jaw, an actuation system comprising a device of the bolt/nut type driven by a motor.
A first system, known and marketed by the applicant, uses a device of the bolt/nut type arranged in a way so as to reproduce the action of a jack, the bolt being driven in rotation by a hydraulic motor via a chain.
This system actuates an assembly of three connecting rods which are linked to each other and two of which have one of their ends connected to a fixed point.
This configuration allows reduction of the clamping force on the flange and tilting of the whole module in order to open or close the coupling.
According to the same principle, a development without connecting rods has been proposed to overcome this drawback while reducing the space requirement and the weight of the device. This development is described in the French Patent Application No. 2834327.
In another device which is already known, the coupling uses compression springs of large diameter each connected at one of their ends to a clamping jaw and at the other to a ring designed to be actuated in rotation.
The inclination of this ring corresponds to the inclination of the springs which, depending on the latter, apply more or less pressure on the clamping jaw which clamps the flange of a complimentary means of the loading arm.
In their compressed position the springs deliver a maximal clamping torque.
The use of a hydraulic jack to activate the ring in rotation means that the mechanism becomes reversible and in the case of a failure of the hydraulic system this can lead to a progressive loosening of the flange.
Another known coupling uses a cam driven in rotation by a hydraulic jack.
This cam applies a load to the clamping jaw to close the coupling and incorporates a parallel irreversibility system in the case of a hydraulic failure.
Another coupling continues the principle of the cam with a toothed rotary washer positioned on the periphery of the coupling. This washer pivots under the pressure of a hydraulic jack and pushes the assembly of the clamping jaw thanks to the teeth which compose it to capture the flange.
According to another existing device, the coupling uses a device of the bolt/nut type, more reliable than a hydraulic jack, to drive the clamping jaw in rotation, the nut being in tilting connection with the latter.
The rotation of the bolt drives the translational movement of the nut which thanks to said tilting connection with the clamping jaw drives the latter in rotation about an axis perpendicular to the axis of translation of the nut, to clamp or release the flange according to the direction of rotation of the bolt.
An emergency release system is provided in parallel, in order to increase the responsiveness of the system during an opening phase in an emergency procedure.
Some known devices, of the same sort as those described above, are in particular disclosed in the patent applications or patents EP-A 0 285 813, U.S. Pat. Nos. 4,222,591, and 3,661,408 and GB-A-1 395 928.
Finally, there exists a coupling device which is known and which is marketed by the Applicant under the name <<Quikcon2>>.
This device has a clamping jaw which combines two movements: a rotation and a translation respectively about and along the same axis.
The clamping jaw overall presents the shape of the letter <<L>>, the base of the <<L>> being the part which effectively serves to grip the flange and its vertical (<<long>>) part corresponding to the axis of said combined rotation and translation.
This last part, which is longer, is introduced into a bore of the frame of the coupling module.
The guiding in rotation of the clamping jaw in this bore is carried out by a ball mounted there between, sliding inside a helical path machined in the <<long>> part of the clamping jaw and held in a specific housing installed in said bore integral with the frame of the coupling module.
The operation of the clamping jaw is carried out using a nut device integral with the clamping jaw and bolt advantageously collaborating with the latter and driven in rotation by an suitable means (hydraulic motor for example).
The bolt and the nut are located in the axis of rotation and translation mentioned above.
In practice, the bolt and the nut are located at the centre of the <<long>> part of the clamping jaw which has a longitudinal bore created for this purpose.
The above-mentioned helical path has a favourable shape which allows transformation of the movement of translation of the clamping jaw imposed by the rotation of the bolt/nut system into a movement of rotation combined with said movement of translation, these two movements occurring respectively about and along the same above-mentioned axis.
Thus, during the closing phase of the clamping jaw a rotation of the latter is initially observed, which rapidly ensures the coupling of the two elements to be coupled, then a translation corresponding to the clamping of said elements together.
The ball is however not designed to withstand high stresses which can, for example, result from an impact between the clamping jaw and an external element.
Thus, the ball can be subject to a permanent deformation or to a mechanical break and the machining of the helical path can also be damaged.
The ball and the helical path can also be damaged by other mechanical stresses due to an opening or a closure in difficult conditions (for example: foreign bodies in the mechanism, corrosion factors, etc.).
In addition, a clamping jaw comprising such helical machining is expensive to manufacture.